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ASSOCIATED EYE CONDITIONS
There are other forms of associated eye conditions that can effect vision and other bodily functions. Degenerative retinal diseases affect millions of people worldwide, causing loss of vision in adults and children alike. The many diseases within this group are caused by any of thousands of known genetic mistakes in approximately 200 genes. Retinitis pigmentosa accounts for about half of all cases of inherited blindness. However, a range of other diseases cause the remaining cases of inherited blindness
Fundus Flavimaculatus is a condition similar to Stargardt Disease but varies in its age of onset and severity. When there is macular damage, vision can deteriorate to 20/200, although it usually remains between 20/50 and 20/80. Damage to the macula first appears in the adolescent and early adult years, and the area of damage may gradually spread.
PIGMENT PATTERN DYSTROPHY
Pigment Pattern Dystrophy, which describes a group of disorders that includes Butterfly shaped Pigment Dystrophy of the fovea, North Carolina Macular Dystrophy, Macro reticular (Spider) Dystrophy and Sjogren Reticular Pigment Epithelium Dystrophy. The macular changes in these patients can occur at any age, but usually first appear in childhood. Many patients do not experience symptoms and may have visual acuities in the 6/6 to 6/24 range. Some of the genes have been identified for these disorders and are located on chromosome 6.
Peripapillary (pericentral) Choroidal Dystrophy is a condition, which causes wasting of the blood vessels that surround the optic nerve. Patients first notice symptoms in the late adult years,
when the macula is affected.
Stationary cone disorders are present at birth and have symptoms decreased acuity, decreased colour vision, sensitivity to light - that do not worsen with age. There are several types of stationary cone disorders (for example, cone monochromatism, blue cone monochromatism, dichromatism, trichromatism) with differing prognoses for visual acuity.
X-LINKED CONE-ROD DYSTROPHY
X-linked Cone-Rod Dystrophy is a rare disorder, and patients present with decreased central vision, may have a bull's eye lesion in the macula, a fine nystagmus, and no or very little pigmentary change in the fundus, until advanced stages of the disease. The visual field loss is slower than in
x-linked RP, the ERG shows a cone-rod pattern if the ERG is recordable, which is often the case: unlike x-linked RP, in which the ERG is severely affected early in the disease.
BEST DISEASE/VITELLIFORM DYSTROPHY
Best disease (also known as vitelliform macular dystrophy) is an inherited form of macular degeneration characterised by a reduction of central vision.
Best disease affects the macula, the central part of the retina responsible for fine visual detail and colour perception. The retina and its component photoreceptor cells are essential to vision as they convert light into electrical impulses and then transfer these impulses to the brain via the optic nerve.
Although the age of onset of Best disease can vary, it is usually diagnosed during childhood or adolescence. In the initial stages, a bright yellow cyst (fluid-filled sac) forms in the retinal pigment epithelium (RPE) beneath the macula. On examination, the cyst looks like a sunny-side-up egg. Despite the presence of the cyst, visual acuity may remain normal or near normal (between 6/9 and 6/18) for many years. Peripheral (side, upper and lower) vision usually remains unaffected.
In many individuals with Best disease, the cyst eventually ruptures. Fluid and yellow deposits from the ruptured cyst spread throughout the macula. At this point the macula has a scrambled egg appearance. Once the cyst ruptures, the macula and the underlying RPE begin to atrophy causing further vision loss. As a result, central vision tends to deteriorate to about 6/36 late in life. However, Best disease does not always affect both eyes equally. Many individuals retain useful central vision in one eye with a visual acuity of about 6/12 in the less affected eye.
In some cases, Best disease does not progress far enough to cause significant central vision loss. However, retinal specialists can still detect the disease using sophisticated diagnostic tests that measure the function of the RPE and the retina. Individuals with Best disease are also often farsighted which can be corrected with glasses.
Best disease is genetically passed through families by the autosomal dominant pattern of inheritance.
Currently, there is no treatment for Best disease. Ongoing scientific research is directed at understanding the cause of Best disease. A gene for Best disease has already been mapped
(located to a specific region) to a human chromosome. Next, this gene will be identified and its function in the retina determined as the first step in developing means of treatment and prevention.
Individuals with Best disease may benefit from the use of low-vision aids and, possibly, orientation and mobility training.
Juvenile retinoschisis is an inherited disease diagnosed in childhood that causes progressive loss of central and peripheral vision (side, upper and lower) due to degeneration of the retina.
Juvenile retinoschisis (also known as X-linked retinoschisis) occurs almost exclusively in males. Although the condition begins at birth, symptoms do not typically become apparent until after the age of 10. About half of all patients diagnosed with juvenile retinoschisis first experience a decline in vision. Other early symptoms of the disease include an inability of both eyes to focus on an object (strabismus) and roving, involuntary eye movements (nystagmus).
The splitting of the retina into two layers causes vision loss associated with juvenile retinoschisis.
This retinal splitting most notably affects the macula, the central portion of the retina responsible for fine visual detail and colour perception. On examination, the fovea (the centre of the macula) has spoke-like streaks. The spaces created by the separated layers are often filled with blisters and ruptured blood vessels that can leak blood into the vitreous body (the transparent, colourless mass of jelly-like material filling the centre of the eye). The presence of blood in the vitreous body causes further visual impairment. The vitreous body degenerates and may eventually separate from the retina. The entire retina may also separate from underlying tissue layers causing retinal detachments.
The extent and rate of vision loss vary greatly among individuals with juvenile retinoschisis.
Central vision is almost always affected. Peripheral vision loss occurs in about half of all cases.
Some affected individuals retain useful vision well into adulthood; with others experience a rapid decline during childhood.
Juvenile retinoschisis can resemble other retinal degenerative diseases such as retinitis pigmentosa (RP), Goldman-Favre viteoretinal dystrophy. Wagner's vitreoretinal dystrophy, and Stickler's syndrome. A thorough eye examination, including diagnostic tests measuring retinal function and visual field, combined with an accurate documentation of family history, can distinguish between these disease.
Juvenile retinoschisis is genetically passed through families by the X-linked pattern of inheritance.
Sometimes, however, when carrier females are examined, the retina shows minor signs of the disease.
At this time, there is no treatment for juvenile retinoschisis. However, in some cases, surgery can repair retinal detachments. Ongoing scientific research is directed at identifying the gene that causes juvenile retinoschisis as the first step in developing means of treatment and prevention. Individuals with juvenile retinoschisis may benefit from the use of low-vision aids, including electronic, computer-based and optical aids, as well as orientation and mobility training.
GENETIC CONDITIONS ASSOCIATED
WITH MACULAR DEGENERATION
Which are caused by the accumulation of drusen, yellow-white deposits, in the macular area.
Drusen deposits usually appear in the first three decades of life, and become larger as a person ages. Decreased vision may not be noticed until the fourth decade, with vision varying between
6/9 and 6/24. If the drusen causes other complications in the retina, vision may decrease to 6/60.
SORSBY MACULAR DYSTROPHY
Which is a rare disorder in which new blood vessels grow under the fovea, resulting in fluid build-up in the macular, haemorrhage, and general wasting of other layers of tissue in the eye. Usually symptoms do not appear until after the age of 40. Drusen may also be present. People with this disorder may experience a rapid decrease in vision. The gene for this disorder has been identified as the TIMP3 gene, which is located on the long arm of Chromosome 22.
PIGMENT PATTERN DYSTROPHY
Which describes a group of disorders that includes Butterfly shaped Pigment Dystrophy of the fovea, North Carolina Macular Dystrophy, Macro reticular (Spider) Dystrophy and Sjogren Reticular Pigment Epithelium Dystrophy. The macular changes in these patients can occur at any age, but usually first appear in childhood. Many patients do not experience symptoms and may have visual acuities in the 6/6 to 6/24 range. Some of the genes have gene identified for these disorders and are located on chromosome 6.